Pluto's occultation on June 22, 2008 observed by Dave Gault

Dave Gault (Sydney Australia) observed the star (2U 25370733) occulted by Pluto. He uploaded the video clip, which records this event as a movie with a chart of light curve obtained from the video, onto Youtube. And he kindly sent me an explanation about his observation and analysis and two graphs of the result.

I am pleased to introduce his outstanding observation on my website as follows.

1.Prediction of this event

The prediction of this event is:

2.Observation by Dave Gault

The video recorded this event is below.

The detail of this observation is described in Daves report on IOTA occultation message board as follows.


Mon Jun 23, 2008 4:30 am

Pluto POSITIVE from The Blue Mountains AUSTRALIA

I just recorded an occultation of Pluto, over 1 minute duration from my

home in the Blue Mountains (west of Sydney). The scopes are still running

so I'll attend the them, and have a celebratory cup of tea! Detail report

to follow!!!






Mon Jun 23, 2008 1:01 pm

Re: Pluto POSITIVE - more detail

David and Salvador,

More info,...

I had two scopes and cameras running side by side.

10"f5 Newtonian, WAT-120N camera and KIWI. 1.28 sec exposure

8"LX90, DSIpro exposure 1 sec every two seconds, saved in FITS

Here is the prediction...

I'll process the FITS tonight. At 113 secs (including atmosphere) I

must have been pretty close to the centre. Maybe something is in the



And he uploaded the video records the occultation by Pluto.


Tue Jun 24, 2008 7:38 pm

Occultation by Pluto, The Movie...


I have uploaded the video to Youtube.

The compression plays havoc but you'll get the idea. The D and the R are

unbelievably s-l-o-w and the star is gone for seemingly an eternity. It was a

jaw dropper seeing it live.

Here is the address.

Popcorn and Coke are freely available in the foyer... :-)





3.Light curve of this event

Below is a light curve the result of analyzing by Dave Gault.

Figure.1 The light curve of Pluto's occultation (blue) and cpmparison star (yellow)

His explanation about how to obtain this data is below.

Note: Several improvement to Dave's original description on his email were done by the author of this website to easily understand the relation between the chart and sentence.


The first pass through Limovie I attempted just after the observation

and before going to work is here. The one at the end of the movie and

the latest version (Figure.1) were treated as I describe below.

Watec WAT-120N video camera can stack in it's memory from 1 frames

(no stacking) to 256 frames. It then outputs the stack at the rate

of 25 frames per second to meet the PAL video standard so that normal

televisions, VCRs, PC TV cards and KIWI OSD will work correctly.

In this case I set the camera to stack 32 frames.

For the light curve of raw data, It shows all frames and if you could

magnify the lines you would see small groups of 32 images. Each image

in the group of 32 should have the same light level but alas noise is

introduced, like tape noise.

For the light curve I have at the end of the video, I used the Limovie

Linked Tracking option to more closely follow Pluto and the target star.

It was particularly helpful to get readings of Pluto when the star was

completely hidden. Then using Excel I identified the groups of 32

frames and averaged each group. I then plotted it in the usual manner.

For the light curve (Figure.1) I repeated the measurement as detailed

in the last paragraph and added a comparison star to alert for biased

readings due to varying sky conditions.

Figure.2 is an image I made at the suggestion of Dave Herald. I

duplicated the curve and flipped it over and over and layed it over

the first. This shows the symmetry of the slight bulges above the

1000 and 1500 scale readings, indicating changes in density in Pluto's




Figure.2 Duplacated the fliped light curve